Hungry Hungry Fungi: How plastic pre-treatments affect fungal interaction with LDPE and PET plastics

I chose to do this project after reading online about a type of fungi discovered in Ethiopia that has the unique ability to be able to break down plastic, this made me curious about whether fungi I could access in Canada might have similar abilities and whether pre-treating plastics such as by abrasion or ultraviolet exposure can increase their susceptibility to fungal interaction. Plastic pollution is a major global issue, with most plastic lasting for decades and accumulating in landfills and our natural environment. However, if the two types of fungi that I will test on (oyster mushrooms and turkey tail fungi) are proven to be effective at biodegrading plastics and can be made even more so, then this idea can be applied as a step to help deal with the management of this worldwide crisis.

The scientific question addressed is: How do different pre-treatments of plastics affect how Pleurotus ostreatus (oyster mushrooms) and Trametes versicolor (turkey tail fungi) interact with LDPE and PET plastics?

For this experiment, it is hypothesized that the abrasion pre-treatment will increase the susceptibility of LDPE and PET plastics to interaction with Pleurotus ostreatus and Trametes versicolor, resulting in greater weakening or mass change compared to untreated and UV-pre-treated plastics. Additionally, Trametes versicolor is expected to be more effective over longer periods due to its enzyme system, while Pleurotus ostreatus may show earlier interaction because of its faster growth rate.

Materials

24 small glass jam containers

Nail

Hammer

Oyster mushroom mycelium block

Turkey tail fungi mycelium block

Latex gloves

Mask

A bottle of 70% isopropyl alcohol

Serrated knife

Paper Towel

Distilled water

Tap water

Ruler

22 paper bowls

An empty Kirkland Signature plastic bottle of water

Tweezers

Amazon plastic packaging

Spray bottle

Scissors

Red permanent marker

Blue permanent marker

Black permanent marker

Grit 220 sandpaper

Digital pocket scale (0.01g precision)

UV nail lamp

Strainer

Pot

Stovetop

Paper

Tongs

Plate

Procedure

First, I obtained twenty-four small glass jars which I then labelled each one with their assigned variables and made two ventilation holes in every lid.

Next, I cut seven approximately 3cm³ pieces from the oyster mushroom and turkey tail fungi mycelium blocks with a sterile knife.

I then placed every fungal block piece into a designated jar according to its variable and watered them daily as a five day pre-growth period.

After that, I cut eleven LDPE plastic pieces, each approximately 5 cm² in size, and I cut eleven PET plastic pieces, each approximately 2 cm² in size. I assigned and applied each piece a pre-treatment which was either no pre-treatment, abrasion, or ultraviolet (UV) exposure.

Additionally, I rinsed every piece in a strainer and once dry, I weighed each piece and recorded the initial mass as Day 0.

Next, I prepared my three types of controls which was a fungi-only control, a heat-killed fungi control, and an abiotic control.

I placed the plastics in their containers, then I took pictures on scheduled days and washed then weighed each piece every two weeks using the same procedure and recorded any data.

The results of this experiment were measured through percentage of plastic mass change over time and through observations of plastic and fungal changes. Measurements of plastic mass were recorded at day 0, day 14, and day 28 for LDPE and PET plastics under abrasion, UV, and no pre-treatment conditions, as well as abiotic and heat-killed controls.

Overall, plastics exposed to living fungi showed decreases in mass over time, while the abiotic controls did not show any mass loss across all plastic types and pre-treatments. This suggests that the mass changes observed in the experimental variables required the presence of living fungi and were not caused by the environment or pre-treatments alone.

Abrasion-treated plastics showed the greatest mass loss compared to UV-treated and untreated plastics. This effect was most noticeable in LDPE samples. By day 28, LDPE plastics exposed to living fungi under abrasion showed larger percentage mass losses than LDPE plastics under UV or no pre-treatment conditions. The single largest mass loss in the experiment occurred in the LDPE with abrasion pre-treatment exposed to Trametes versicolor.

However, Trametes versicolor did not show consistent mass loss across all conditions. In all of the PET variables, Trametes versicolor showed no mass loss by day 28, and in some cases the mass returned to the original day 0 value after initially decreasing. Because of this, Trametes versicolor cannot be considered more effective overall, but instead showed its strongest interaction under specific conditions, with the abrasion pre-treatment LDPE.

Pleurotus ostreatus showed a more consistent pattern of mass loss across the experiment. It showed measurable mass decreases in LDPE under abrasion, UV, and no pre-treatment, and also showed mass loss in PET under all three pre-treatments by day 28. While the percent mass loss was smaller than the largest Trametes versicolor result, Pleurotus ostreatus interacted with both plastics more consistently within the 28-day period.

When comparing plastic types, LDPE generally showed greater and more frequent mass loss than PET across all conditions. PET showed smaller overall changes and remained unchanged in several variables, indicating that PET was more resistant to fungal interaction within the time frame of this experiment.

Visual observations supported the mass change data. Plastics exposed to living fungi showed surface interaction on all samples, with abrasion-treated plastics appearing to show more visible surface changes. Pleurotus ostreatus showed much more visible mycelium and fruiting body growth than Trametes versicolor, although greater visible growth did not always correspond to greater mass loss. Abiotic controls did not show fungal growth or plastic interaction. The heat killed fungi control did not produce mycelium but instead developed mold, which likely made plastic mass percentage change unreliable due to the control still having living fungi.

In conclusion, the results suggest that abrasion pre-treatment increased the susceptibility of LDPE and PET plastics to fungal interaction, supporting the hypothesis. LDPE was more affected than PET. Trametes versicolor produced the largest single mass-loss result under abrasion-treated LDPE, while Pleurotus ostreatus showed the most consistent mass loss across plastic types and pre-treatments. Although the plastics were not fully degraded, the experiment demonstrated measurable plastic mass changes and surface interaction under specific conditions.

This project could be expanded and applied as a biodigester, where a tank is filled with oyster mushrooms or turkey tail fungi under ideal growing conditions and plastic waste is placed inside to biodegrade. Abrasion pre-treatment could be applied automatically by adding a grinder leading into the tank before the plastic enters. This experiment could be improved by using a higher-precision scale to reduce measurement uncertainty caused by small mass changes. Testing each variable more could help better demonstrate patterns of data and cutting fungi chunks to more equal sizes would improve consistency in enzyme production.

I would like to acknowledge my school, King's Edgehill, for all the support. It's a community where ideas like mine can grow. I would like to thank my teachers, particularly Ms. Cecchetto, Mr. Wilt, and Mr. Kershaw for their guidance and inspiration. This project would not be possible without the encouragement and emotional support from my family during the countless hours of development.

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